Are you seeking plants that will grow under the Black Walnut trees on your property? Black walnut trees can be a tricky plant for gardeners, as this species of plant produces a toxic substance called juglone via its root system. Other trees that emit this toxic substance include butternut and Persian walnut trees that are grafted with black walnut. (Notably, persian walnut seedlings that are grafted onto persian walnut rootstocks do not produce deadly toxins that kill other plants.) The juglone leaches out into the surrounding soil and it can kill nearby plants within a period of just 30 to...